How we keep data current

Rates, thresholds and rules in New Zealand change throughout the year. Keeping 1,169 calculators accurate is a managed, repeatable process, not an occasional tidy-up. This page sets out exactly how it works.

Maintaining data accuracy at this scale is a data-management discipline. The process below follows the same practices used to keep any trusted dataset reliable: a defined source of truth, a register that maps every figure to its authoritative source, scheduled change detection, controlled updates, validation, and a visible audit trail.

The twice-monthly review cycle

Twice a month, every authoritative source on our register is checked for change. The review runs on a fixed fortnightly cadence so nothing depends on chance discovery, and the date of each review is recorded.

1. 1. Scan the source register. Each source on the register (see below) is checked for new rates, thresholds, legislation, determinations or published figures since the last review. Findings, including "no change", are logged so the absence of an update is itself recorded.
2. 2. Triage what changed. Any change is assessed for impact: which calculators, guides and datasets depend on that figure, how material the change is, and when it takes effect (some changes are dated for a future start, such as a 1 April rate).
3. 3. Update the single source of truth. Shared figures live in central data files, so a rate is defined once. The change is made there and flows automatically to every tool that references it, which removes the risk of updating one calculator and missing another.
4. 4. Validate. Worked examples are re-checked so each tool's output still matches its source, and automated checks run across the library to catch broken logic, missing structured data or values that drifted.
5. 5. Record and date. The update is version controlled with a dated entry, the affected pages carry a last-reviewed date, and the change is reflected in the public library history.

Principles behind the process

• Single source of truth. Each rate or threshold is stored once and reused everywhere, so the whole site moves together when it changes.
• Data separated from presentation. The numbers live in data files, not buried inside individual pages, which makes them auditable and safe to update at scale.
• Provenance. Every figure is traceable to the official source it came from, so it can be re-verified rather than taken on trust.
• Scheduled change detection. A fixed fortnightly cadence plus event triggers, rather than waiting for someone to notice.
• Validation before publish. Worked-example checks and automated tests confirm a change is correct before it goes live.
• Visible freshness. Last-reviewed dates and a public change history show the work, rather than asking you to assume it.

Event triggers between scheduled reviews

Some dates always warrant a fuller review, and these are handled as they occur rather than waiting for the next cycle:

• The 1 April tax-year rollover, when many IRD rates, thresholds and ACC levies change.
• The annual Budget in May, and any in-year tax or benefit announcements.
• Official Cash Rate decisions and other RBNZ updates that affect interest and mortgage tools.
• Minimum wage changes, benefit and superannuation adjustments, and new or amended legislation.

The sources we track

Source	What we track from it
Inland Revenue (IRD)	Income tax brackets, PAYE, GST, ACC earner rates, KiwiSaver settings, student loan thresholds, FBT, RWT, Working for Families, FIF rules
Reserve Bank of New Zealand (RBNZ)	Official Cash Rate, LVR and DTI settings, published interest rate data
Stats NZ	Inflation (CPI), wage and earnings data, household statistics
MBIE	Minimum wage, tenancy and employment settings
Ministry of Social Development (MSD)	Benefit rates, NZ Superannuation, accommodation support
Waka Kotahi NZ Transport Agency	Road user charges and vehicle-related figures
Legislation	The underlying Acts and regulations that define the rules each tool implements

If something is still wrong

No process is perfect. If you spot a figure that looks out of date or incorrect, please tell us and it will be checked and corrected promptly. How the tools are built is set out in our editorial standards.

Review cadence: twice monthly. This page last reviewed 2026-06-02. Maintained by James Graham.